1. Field of the Invention
The present invention relates to an elevator adjusting apparatus, and more particularly to an apparatus capable of adjusting a brake torque.
2. Description of the Related Art
One conventional elevator adjusting apparatus of the above type is disclosed in Japanese Patent Laid-Open No. 1-197290 which corresponds to U.S. Pat. No. 4,984,659.
FIG. 9 is a front view showing an electromagnetic brake integrally assembled to a hoist of an elevator in the prior art.
In the drawing, denoted by reference numeral 50 is a pair of brake levers each of which is normally biased by a spring 51 in the direction of arrow A. 52 is a brake shoe attached to each of the brake levers 50; 53 is a brake wheel rotating together with a electric motor (not shown); and 54 is a rotatable shaft directly coupled to the electric motor (not shown), the brake wheel 53 being fixed to the rotatable shaft 54. A substantially L-shaped cam 55 turns in the direction of arrow B upon movement of the brake lever 50 in the direction of arrow A. A plunger 56 is held in abutment against distal ends of the cams 55 and 57 is a brake coil for attracting and moving the plunger 56 upon supply of electric power.
In the electromagnetic brake thus arranged, the brake levers 50 are normally biased by the springs 51 in the directions of arrows A,.respectively. This biasing causes the brake shoes 52 to grasp the brake wheel 53 for arresting its rotation. In this state, the cams 55 are turned in the directions of arrows B to push up the plunger 56. When electric power is supplied to the brake coil 57, the plunger 56 is attracted by the brake coil 57 to descend. With such a descent, the cams 55 are turned in the directions of arrows C, whereby the brake levers 50 are turned in the directions of arrows D against the urging forces of the springs 51. Upon the brake levers 50 being turned in this way, the brake shoes 52 release the brake wheel 53 from its arrested state. As a result, the rotatable shaft 54 can be driven by the electric motor to ascend or descend the elevator on demand.
This type braking mechanism is indispensable from the viewpoint of securing safety of elevators, and all the load is applied to the brake when the elevator is stopped. At this time, if a brake tightening torque is not sufficient, the brake would cause a slip, which is seriously dangerous. Conversely, if the brake tightening torque is too strong, a stop shock would be very large when the elevator is quickly stopped, which is also dangerous. For that reason, it is required to appropriately adjust such a brake tightening torque. As used herein the term "brake tightening torque" (hereinafter referred to simply as a brake torque) is defined as the movement exerted by a braking mechanism about a shaft necessary to prevent the elevator cage from slipping when the shaft is not rotating.
Heretofore, the brake torque has been adjusted by a method of once loading a weight on the order of 125% of the cage load, and adjusting the biasing forces of the springs 51 in a machinery room so that the brake does not slip. Thus, the conventional elevator adjusting apparatus adopts the electromagnetic brake as a braking mechanism, and the weight on the order of 125% of the cage load must be loaded on the cage in the conventional method of adjusting the brake torque. Additionally, after completion of the adjustment, the weight must be unloaded from the cage, meaning that a great deal of labor and time are necessary.
Furthermore, because the conventional adjusting method only adjusts the brake torque in such a manner as to prevent a slip of the brake, the brake may be often tightened too strong or too weak. Thus, it has not been easy to adjust the brake torque in conformity with desired standards.